Hey, nice to see life drawings. Try to do many of these, they help a lot.
Don't hesitate to at least indiquate with a cross the center line of the face and the eye lines. The ear is also a nice feature to indiquate how the head turns. Don't try to detail the face for quick poses, jsut indiquate it's basic orientation.
Do you start the drawings by the head, or something else? try to start by spotting the orientation of the shoulders and the hips. Pay attention to how the body rest on the ground on its standing points, the feets, or the hands. Think about balance and weight.
Try not to jump to detail on short poses, concentrate on rythm flow and proportions. For very short poses, like 30 secondes to 1 minutes, you can concentrate only on the rythm of the pose, and not try to have the perfect proportions...
For longer poses, 5 minutes and up, don't forget that a human body is not flat like a piece of paper, but has a front, side, and back. Try to sense the volume, think of boxes and cylinder to spot how the forms are in perspective from your point of view.
Don't hesitate to learn anatomy, like the skeleton and apparent muscles, and how they can move in space, and apply that to the live drawings.
Combining both, anatomy and observation, structure and rythm and flow, will improve your drawings. It's hard, but with practice and time you will find it will become a second nature.
For long poses, don't hesitate to turn around the model, and draw the same pose from multiple point of vue.
Carry a sketchbook and do some sketch in streets, too.
Your drawings are nice, just go on and do more. You'll improve with the years, just try to do some each week. it's like playing a guitar :)
Micheal Di Mattesi wrote a very good book on that subject: "Force", which I higly recommend. He gave drawing classe in animation studios like dreamworks.
(Sorry for the long post, I do life drawings since more than ten years now and I just wanted to throw in my two cents, hope it will help)